The present invention relates to the analysis of frequency domain data, and more particularly to automatic generation of a frequency domain mask for pass/fail analysis of frequency domain data.
Some frequency domain instruments, such as radio frequency (RF) spectrum analyzers, while displaying frequency domain traces for a signal, also support an optional display of a pass/fail mask shape while the instrument is acquiring the signal. If any part of the frequency spectrum of the signal is above the mask (“upper limit” mask) or below the mask (“lower limit” mask), the instrument uses some means for alerting a user about the mask failure, such as by providing a warning light, message on the display, beep, saving a data file for the signal, etc. Most masks in common use are specified manually by the user, i.e., by drawing lines in a user interface window, entering numeric values from a keyboard, etc. Alternatively the mask may be chosen from manufacturer provided preset values, such as a channel mask for a given signal standard.
A more flexible alternative for generating masks is to acquire some representative real-world signal and invoke an auto-generation function to build a mask that conforms to the shape of the sampled frequency domain data for the signal, but is spaced from it by a user-specified frequency offset in one direction, such as the X-axis, and amplitude offset in the orthogonal direction, such as the Y-axis. Auto-generation techniques for masks typically generate only one kind of mask at a time, usually an upper limit mask. One example is the Y400/YBT250 RF Scout® Interference Hunter spectrum analyzer manufactured by Tektronix, Inc. of Beaverton, Oreg. which uses X and Y offsets together in one drawing phase.